DAG-SFC: Minimize the Embedding Cost of SFC with Parallel VNFs

Network Function Virtualization (NFV) is an emerging technology, which enables service agility, flexibility and cost reduction by replacing traditional hardware middleboxes with Virtual Network Functions (VNFs) running on general-purpose servers. Service Function Chain (SFC) constitutes an end-to-end service by organizing a series of VNFs in a specific order. Particularly, hybrid SFC (SFC with parallel VNFs) is proposed to much reduce the traffic delay in sequential SFCs. Nevertheless, how to strategically select VNF instances and links in hybrid SFC embedding remains an open problem. In this paper, we target at the cost minimization and address the optimal hybrid SFC embedding problem. Specifically, we first develop a novel abstraction model for the hybrid SFC with Directed Acyclic Graph (DAG), which helps convert diverse hybrid SFCs to the standardized DAG-SFC form. Then, we formulate the optimal DAG-SFC embedding problem as an integer optimization model and propose a greedy method (called BBE) to solve the NP-hard problem. MBBE method is developed upon BBE method to further cut down the computation complexity in model solving. Extensive simulation results demonstrate the effectiveness of our approach for cost reduction in hybrid SFC embedding.